Recently, a technology utilizing renewable resources (biomass) has attracted attention from a viewpoint of suppression in global warming and in use of depleting resources. As a plastic, polylactic acid has attracted attention as a plastic produced by using a plant as a raw material (hereinafter, referred to as a plant-derived plastic). Lactic acid to be used as a raw material is obtained by fermenting starch of corn, sweet potato, or the like. However, polylactic acid often has degraded mechanical strength and heat resistance compared to those of a conventional plastic, and use of polylactic acid has been limited to a packaging material, tableware, and the like.
An object of the invention described in Japanese Patent Application Laid-Open No. H11-140292 is to provide a polylactic acid-based resin composition having maintained characteristics of polylactic acid such as excellent biodegradability, mechanical strength, heat stability, and transparency, and improved brittleness of polylactic acid, and a method of producing the same. Another object of the invention described in Japanese Patent Application Laid-Open No. 11-140292 is to provide a packaging material or various molded products each formed of the polylactic acid-based resin composition.
Further, U.S. Pat. No. 2,551,731 and Y. Hachihama, T. Shono, and K. Hyono, Technol. Repts. Osaka Univ., 8, 475 (1958) each substantially describe the following skeleton structure.

Of the documents, Y. Hachihama, T. Shono, and K. Hyono, Technol. Repts. Osaka Univ., 8, 475 (1958) describes studies in effects of the number of methylene chains of α,ω-glycol on a melting point of a produced polymer compound in polycondensation of 2,5-furandicarboxylic acid and α,ω-glycol by conducting polycondensation with a varying number of methylene chains of α,ω-glycol.
U.S. Pat. No. 2,551,731 describes experimental conditions for synthesis of a polyester having a heterocyclic ring in a skeleton of a polymer compound, and an yield of the polymer compound.
U.S. Pat. No. 2,551,731 and Y. Hachihama, T. Shono, and K. Hyono, Technol. Repts. Osaka Univ., 8, 475 (1958) each describe the skeleton structure described above, but include no description of the number of units.
Such a skeleton structure is described, but physical properties described in Y. Hachihama, T. Shono, and K. Hyono, Technol. Repts. Osaka Univ., 8, 475 (1958) (see FIG. 1 of p. 479, for example), for example, refer to a melting point alone. Mechanical strength is not revealed, and whether the skeleton structure can be used for applications of electric and electronic components and the like is not clarified.